1,2-Bis(mercaptoacetamido)ethane (commonly referred to as DADS) is a tetradentate chelating agent which has been evaluated as a technetium-99m renal function radiopharmaceutical. See A. R. Fritzberg et al, J. Nucl. Med. 22: 258-263, 1981. Biological studies have indicated that this agent is cleared by the kidneys significantly faster than Tc-99m diethylenetriaminepentaacetic acid (Tc-99m DTPA, p&lt;0.01) and slightly slower than I-131 o-iodohippurate (p&gt;0.05), with no evidence of significant renal retention. While this agent has shown promise as an imaging agent for the renal system there is need for such agents with higher extraction efficiency.
Ideally, renal function should be evaluated with a single radiopharmaceutical which possesses high extraction efficiency, such as I-131 o-iodohippurate (OIH), and also is labeled with a radionuclide having good physical properties such as technetium-99m. Currently two agents are commonly used in the evaluation of renal function, OIH and Tc-99m DTPA. Renal perfusion is evaluated by rapid serial imaging during the first circulation after bolus injection of Tc-99m DTPA. OIH cannot be used for this purpose because the iodine-131 label limits the amount of radioactivity that can be injected. Renal clearance can be evaluated with either Tc-99m DTPA or OIH, but since Tc-99m DTPA is limited to clearance by glomerular filtration, the maximum extraction efficiency is 20%. Secretion of OIH by the renal tubular cells, in addition to some filtration, results in extraction efficiency of about 67%. The higher extraction efficiency of OIH increases the kidney-to-background image ratio, thus increasing the sensitivity of OIH for detection and evaluation of reduced renal function. Davison and coworkers J. Nucl. Med. 20: 641, 1979; Inorg. Chem. 20: 1629-1632, 1981, have described the benzoyl-protected dimercaptodiamides (PhCOS(CH.sub.2).sub.n CONH).sub.2 X (n=1, X=(CH.sub.2).sub.2, (CH.sub.2).sub.3, and o-C.sub.6 H.sub.4 ; n=2, X=(CH.sub.2).sub.2 and (CH.sub.2).sub. 3). From these, via the sodium dithionite reduction of TcO.sub.4.sup.- in base, the technetium complexes [TcO(S(CH.sub.2).sub.n CONXNCO(CH.sub.2).sub.n S)].sup.- (n=1, X=(CH.sub.2).sub.2, (CH.sub.2).sub.3, and o-C.sub.6 H.sub.4 ; n=2, X=(CH.sub.2).sub.2) were prepared. The synthesis and characterization of the complexes, and their precursors, were reported, and their radiopharmaceutical applicability was discussed.